Synaptopodin regulates denervation-induced plasticity at hippocampal mossy fiber synapses

Neurological diseases can lead to the denervation of brain regions caused by demyelination, traumatic injury or cell death. Nevertheless, the molecular and structural mechanisms underlying lesion-induced reorganization of denervated brain regions are a matter of ongoing investigation. In order to address this issue, we performed an entorhinal cortex lesion (ECL) in mouse organotypic entorhino-hippocampal tissue cultures of both sexes and studied denervation-induced plasticity of mossy fiber synapses, which connect dentate granule cells (dGCs) with CA3 pyramidal cells (CA3-PCs) and play important roles in spatial learning. Partial denervation caused a strengthening of excitatory neurotransmission in dGCs, in CA3-PCs, and their direct synaptic connections as revealed by paired recordings (GC-to-CA3). These functional changes were accompanied by ultrastructural reorganization of mossy fiber synapses, which regularly contain the plasticity-related protein synaptopodin and the spine apparatus organelle. We demonstrate that the spine apparatus organelle and its integral protein synaptopodin are associated with ribosomes in close proximity to synaptic sites and unravel a synaptopodin-related transcriptome. Notably, synaptopodin-deficient tissue preparations that lack the spine apparatus organelle, failed to express lesion-induced synaptic adjustments. Hence, synaptopodin and the spine apparatus organelle play a crucial role in regulating lesion-induced synaptic plasticity at hippocampal mossy fiber synapses.